Method of making gaseous glow tubes



Jan. 24, 1961 J. H. MCCAULEY 2,969,270

METHOD OF MAKING GASEOUS GLOW TUBES PIC-3.3

Filed Sept. 3, 1957 ASSE M BLE TUBE EVACUATE. AND

FILL W\TH GAS APPLY HxeH REVERSE VOLTAGE AND CURRE MT To AGE. GAS

APPLY SAME VOLTAGE AND LOWER CURRENT TO AGE CATHODES AND GAS FIG.Z

INVENTOR. JOHN H. McCA/JLEy METHOD OF MAKING GASEOUS GLOW TUBES John H. McCauley, Elizabeth, N.J., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Sept. 3, 1957, Ser. No. 681,637

7 Claims. (Cl. 316-26) This invention relates to gaseous indicator glow tubes and particularly to improved methods of preparing such tubes.

Gaseous glow tubes of the type contemplated by the present invention generally comprise a transparent envelope which contains an anode electrode, at least one cathode glow electrode and a gas suitable for supporting cathode glow. When a suitable electrical potential is applied between the anode and the cathode electrode, the cathode glows and space current flows through the gas from the cathode to the anode. Generally, in the initial step in processing or aging such tubes after the tube components have been assembled, a comparatively large Voltage and current are applied between the anode and cathode in normal operating polarity so that the cathode electrode glows. \This processing step is generally utilized to purify the gas filling of the envelope and to stabilize the operating condition of the cathode electrodes. However, during this aging process, cathode metal sublimes from the glowing cathode and the life of the cathode may thereby be considerably shortened, particularly if the cathode is thin and comparatively fragile. In addition, the tube lead and pin connected to the cathode glow during aging and this glow cannot always be eliminated by subsequent processing.

Accordingly, one object of the present invention is to provide an improved gaseous glow tube and an improved method of making the same.

Another object of the invention is to provide an improved method of making a gaseous glow tube which is fast and efiieient and provides improved operation of the tube electrodes.

In brief, a method of preparing a gaseous indicator glow tube according to the invention comprises mounting cathode and anode electrodes in an envelope and filling the envelope with a suitable gas under pressure. The method is particularly effective where the anode is a comparatively large-area electrode. The process of the invention comprises applying a large activating voltage and current between the anode and cathode(s) which is reversed in polarity from the normal operating voltages and currents which are ordinarily employed in operating the tube so that the anode is operated as a cathode and glows and the cathode is operated as an anode and does not glow. This initially applied voltage and current causes the removal of impurities from the gas and the entrapment of these impurities by the normal anode electrode and the other internal tube elements. After the tube has been satisfactorily initially activated in the foregoing manner, the voltage and current are reversed, the current being diminished to close to normal operating value, to provide the normal operating polarity. The cathode electrode or electrodes are thus caused to blow and become aged and the tube is processed to completion.

The invention is described in greater detail by reference to the single sheet of drawings wherein:

Fig. 1 is a perspective view, partly in section, of a gaseous indicator tube prepared according to the method of the invention;

Fig. 2 is a flow chart of the steps of the method of the invention; and

Fig. 3 is a schematic representation of a portion of the tube of Fig. 1 and electrical apparatus used in the preparation thereof.

Referring to the drawings, a typical gaseous indicator glow tube 10 prepared according to the invention includes an envelope 12 which has been evacuated of air and filled with a gas such as neon or the like at a suitable pressure. The envelope includes a base portion, or stem 14, through which metal base pins 16 extend and by means of which electrical connection is made to suitable external electrical circuit elements. Two diametrically opposed pins 16 are provided with extension posts 18 within the envelope and are adapted to receive and support the various electrode elements of the tube. The envelope 12 also includes a transparent viewing window 20 through which glowing indicator cathode electrodes 22 are viewed. A sealed off exhaust tabulation (not shown) is provided in the stem 14.

The indicator cathode electrodes 22 of the tube 16 may take substantially any desired shape; for example, they may be numbers, letters, or the like, and they may be as few in number as desired, or as many as is practical for the size of the tube. Such cathodes are comparatively fragile and have small surface areas. In one form of the tube 19 wherein the cathode elements are numbers, ten of such elements are provided, including the numbers 0 to 9. Only three cathodes are shown in Fig. 1 for purposes of simplification of the drawing. The cathode elements 22 are made of any suitable metal, for example, stainless steel, aluminum, nichrome, molybdenum, or the like, and they may be made in any suitable fashion, for example, by etching, stamping, or the like.

The cathode elements are provided with diametrically opposed apertured end tabs (not shown) by means of which they are mounted and supported on the extension posts 18 of the pins 16'. The cathode elements 22 are stacked on the posts 18 one above the other with their surfaces oriented parallel to each other transverse to the vertical axis of the tube and facing the viewing window 20 of the envelope 12. The cathode elements 22 are mounted with suitable insulating spacers 24 between them, the spacers being larger than the tabs and having sufiicient surface area to cover and insulate the cathode tabs to prevent them from glowing. The stack of electrodes is locked on the posts by mica rings 26.

Each cathode indicator element is provided with a fine wire connecting lead 28 which is welded or otherwise secured at its free end to one of the pins 16 within the envelope 12. The leads 28 may be of the same material as the numbers or they may be of any other suitable material.

An anode assembly is also provided in the tube 19. The anode assembly is preferably mounted in the stack of cathode elements and may take many forms. In the tube 10 shown in Fig. 1, the anode comprises two comparatively fine mesh screens 32 and 34, one of which 32 is mounted at the top of the stack of numbers and other of which 34 is disposed between two cathode elements at about the middle of the stack. The two screens are insulated from the cathodes by washers or spacers 24 just as the cathodes are insulated from each other. The anode screens are suitably electrically connected together by a fine wire lead (not shown) which may extend vertically between them and is secured to each of them without touching a cathode. The anode assembly is also electri' cally connected to one of the pins 16 and it may be desirable to coat the anode lead and pin with a layer (not shown) of a suitable material, such as aluminum oxide, 9. glass frit, or the like, to insulate them from the other leads and pins. Of course, a single anode screen may also be employed.

A cup-shaped electrode 36 having a large surface area is provided and is utilized as part of the anode of the tube. The stack of cathodes 22 and the anode screens 32 and 34 are carried inside the cup and are shielded thereby. The cup 36 rests on, but is insulated from, the pins 16 by an insulating disk 38, for example, of mica. In operation of the tube 10, the cup electrode 36 may be maintained electrically neutral or it may be operated as part of the anode.

According to the method of the invention, the tube is prepared as follows referring to the flow chart of Fig. 2. First, the cathode indicator electrodes 22, the anode screens 32 and 34, and the cup electrode 36 are assembled on the tube stem 14, and the stem and envelope 12 are sealed together. The envelope and its contents are then baked and exhausted according to standard techniques and the envelope is filled with a suitable gas, such as neon, at a suitable pressure, for example, about 100 mm. Hg.

Next, as shown in Fig. 3, a suitable power source, for example, a battery 49 is connected across the tube 10, for example, through a double pole double throw switch 42 with the positive terminal connected to one or all of the indicator elements (one indicator 2 is shown) which is thus operated as the anode and the negative terminal is connected to the cup electrode 36 which is thus operated as the cathode. A large voltage and current of the order of 300 volts and 8 milliarnperes, respectively, are thus applied to the tube as the initial aging step. This operation causes the cup operated as the cathode to glow brightly and removes impurities from the gas, the impurities being trapped in the large area surface of the cup electrode and on the envelope wall and the like. This step is continued until the color of the gas signifies that a state of high purity has been reached. A time of about 10 minutes has been found to be satisfactory for neon gas at the indicated pressure in a tube having a height and diameter of about one inch.

In the next step in the aging process, the voltage is reversed so that the indicator electrodes 22 are operated in their normal fashion as cathodes and the cup electrode is operated in normal fashion as the anode. The voltage is maintained at about 300 volts but the current is reduced to about 2 milliamperes. This step serves to age the cathode indicator elements and to further age or purify the gas and is continued for a comparatively long time, for example, 48 hours. At the end of this time, the oathode electrodes have reached a stable operating state and the gas is properly aged or purified. Of course, the voltages and currents and times of application thereof may be varied as required.

It is clear that other gases than neon, for example argon, krypton, or the like may be used and the gas pressures may be varied within the scope of the invention. In addition, the principles of the invention are applicable to gaseous glow tubes of all sizes and materials.

The method of the invention thus provides a gaseous glow tube containing a gas which has been properly aged and a cathode or cathodes which are intact and which have been properly aged without being adversely affected by the aging process. In addition, while the glow cathodes have been processed to a state where they glow readily, there is substantially no glow in the leads and pins connected to the cathodes.

What is claimed is:

1. The method of making a gaseous glow tube of the type comprising an envelope containing a gas, a cathode elect-rode adapted to glow and an anode electrode, said method comprising the steps of mounting said cathode and anode in said envelope, filling said envelope with a gas for promoting the glowing of said cathode, applying a voltage between said cathode and anode of such polar- .ity thatsaid anodeis operated as acathode and :saidcathode is operated as an anode and thereby causing said axode to glow and said anode absorbs impurities from said gas, and then applying a voltage between said electrodes of reverse polarity so that said cathode is operated as a cathode and said anode is operated as an anode whereby said cathode glows and is conditioned for normal glow operation.

2. The method of making a gaseous glow tube of the type comprising an envelope containing a comparatively pure gas of the type capable of sustaining the glow of a cathode electrode, said method comprising the steps of mounting a comparatively small and fragile indicator glow electrode and another electrode having a large surface area in said envelope, filling said envelope with said gas in a relatively impure state, and removing impurities from said gas onto said large area electrode by operating it as a cathode with respect to said indicator glow electrode, and then causing said small electrode to glow and become conditioned for normal operation.

3. The method of making a gaseous glow tube of the type comprising an envelope containing a gas, a cathode electrode adapted to glow and an anode electrode, said method comprising the steps of mounting said cathode and anode in said envelope, filling said envelope with a gas for promoting the glowing of said cathode, applying a unidirectional voltage of about 300 volts between said cathode and anode of such polarity that said anode is operated as a cathode and said cathode is operated as an anode and a current of about 8 milliamperes flows. and then reversing the polarity of said voltage so that said cathode is operated as a cathode and said anode is operated as an anode and reducing the current flow to about 2 milliamperes.

4. The method of making a gaseous glow tube of the type comprising an envelope containing a comparatively pure gas of the type capable of sustaining the glow of a cathode electrode, said method comprising the steps of mounting a comparatively small and comparatively fragile electrode and another electrode having a large surface area in said envelope, filling said envelope with said gas in a relatively impure state, applying a voltage between said electrodes such that impurities from said gas deposit on said large area electrode, and then reversing the polarity of said voltage between said electrodes and thereby conditioning said fragile electrode for glow operation.

5. The method of making a gaseous glow tube of the type comprising an envelope containing a comparatively pure gas of the type capable of sustaining the glow of a cathode electrode, said method comprising the steps of mounting a comparatively small and fragile electrode and another electrode having a large surface area in said envelope, filling said envelope with said gas in a relatively impure state, applying a larger-than-normal unidirectional voltage between said electrodes of such polarity that said large surface area electrode is the cathode and glows and said small electrode is the anode and a large current flows between them, and then reversing the polarity of said volt age and the flow of current and reducing the magnitude of said current, and maintaining said reduced current until said small electrode is conditioned for glow operatron.

6. The method of making a gaseous glow tube of the type comprising an envelope containing a gas, a smallarea cathode electrode adapted to glow and a large-area anode electrode, said method comprising the steps of mounting said cathode and anode in said envelope, filling said envelope with a gas for promoting the glowing of said cathode, applying a first unidirectional voltage between said cathode and anode of such polarity that said anode is operated as a cathode and glows and said cathode is operated as an anode and does not glow, maintaining said first voltage until impurities are removed from the gas and the gas glows with its characteristic color, and then applying a second unidirectional voltage between said electrodes of reverse polarity so that current flows between said anode and cathode and said cathode is operated as a cathode and glows and said anode is operated as an anode and does not glow, the glow of said cathode being at a higher-than-normal level to cause said cathode to be aged and to become stabilized for subsequent normal operation of the tube.

7. The method of making a gaseous glow tube of the type comprising an envelope containing a gas, a plurality of small-area cathode electrodes adapted to glow and a large-area cup-shaped anode electrode, said method comprising the steps of mounting said cathodes and anode in said envelope with said cathodes being positioned within the cup-shaped anode, filling said envelope with a gas for promoting cathode glow, applying a first unidirectional voltage between said anode and at least one cathode of such polarity that said anode is operated as a cathode and glows and said cathode is operated as an anode and does not glow, maintaining said first voltage until impurities are removed from the gas and the gas glows with its characteristic color, and then applying a second unidirectional voltage between said electrodes of reverse polarity so that current flows between each of said cathodes and said anode so that said cathodes are operated as cathodes and glow and said anode is operated as an anode and does not glow, the glow of said cathodes being at a higher-than-normal level to cause said cathodes to be aged and to become stabilized for subsequent normal operation of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,134,710 Eitel et a1. Nov. 1, 1938 2,677,071 Caine Apr. 27, 1954 2,774,645 Batchelor Dec. 18, 1956 2,845,324 Heney et al July 29, 1958 FOREIGN PATENTS 601,870 Great Britain May 13, 1948 

